The kidneys play many vital roles in homeostasis. They filter all the blood in the body many times each day and produce a total of about 1.5 liters of urine. The kidneys control the amount of water, ions, and other substances in the blood by excreting more or less of them in urine. The kidneys also secrete hormones that help maintain homeostasis.

Erythropoietin, for example, is a kidney hormone that stimulates bone marrow to produce red bloodcells when more are needed. The kidneys themselves are also regulated by hormones.

For example, antidiuretic hormone from the hypothalamus stimulates the kidneys to produce more concentrated urine when the body is low on water.

Summary

The kidneys maintain homeostasis by controlling the amount of water, ions, and other substances in the blood.